1. Filed of the Invention
The present invention generally relates to a high-frequency (hf) resectoscope implement to cut body tissue in a body cavity filled with an electrically conducting fluid, such as the human bladder. More particularly, the present invention is directed toward an hf resectoscope implement having a loop support and a loop-shaped cutting electrode mounted distally to the loop support, wherein a plane of the electrode slants relative to a longitudinal axis of the loop support.
2. Description of Related Art
Conventional resectoscopes make use of the mono-pole technique, wherein an hf current is set up between the resection electrode, which is the active electrode, through the body of the patient and a neutral electrode of substantial surface, which is mounted externally on the patient, for instance on the thigh.
However, passing current through the patient""s body entails certain risks which, even when the resectoscope is expertly handled, can never be completely eliminated. For instance, uncontrolled or stray leakage currents may lead to painful skin bums on the patient when the patient contacts a metallic object such as the operating table. If there are current-induced muscle contractions, there is danger that the patient will move in an uncontrolled and sudden manner and, thus, be subjected to unintended cutting injury by the resectoscope implement. Latently, there is also a danger that the muscles or nerves near the resection area may be damaged, at least temporarily, by stray currents.
The above dangers can be widely eliminated using bi-polar techniques wherein both the active electrode and the neutral electrode are inserted into the patient""s body. As a result, the hf current is set up only between the two implement electrodes, but not, and if so only over defined short paths, through the body of the patient.
A bi-polar hf resectoscope implement is disclosed in the German Offenlegungsschrift 25 21 719, which is considered the nearest state of the art. Therein, the neutral electrode is mounted at the loop support arm and together with the loop support arm can be axially moved into and out of the stem of a resectoscope. This feature offers the advantage that the spacing between the active and neutral electrodes remains constant and that, accordingly, the current paths are also substantially constant. Therefore, the cutting action of the cutting electrode is approximately constant at any advanced position of the implement.
As regards implements of this kind, the neutral electrode is in the fluid and spaced from the body tissue. When the active electrode makes contact with the tissue, the hf current passes through the body tissue and then into the fluid and from the fluid back to the neutral electrode.
However, the bi-polar technique incurs problems of current losses arising from current passing directly through the electrically well-conducting fluid between the active and the neutral electrodes without passing through the body tissue. Consequently, only a portion of the current applied to the hf implement will effect the cutting by the active electrode, namely that portion which passes from the active electrode into the body tissue and from there back to the neutral electrode.
These current losses are amplified especially if the intervention takes place in body cavities containing an especially electrically well-conducting fluid. This may occur, for instance, when resection rinsing is carried out using a fluid rich in electrolyte, illustratively an isotonic fluid. In such cases even the major portion of the current goes straight from the cutting site, that is, from the active electrode to the neutral one, without contributing to cutting. Accordingly, cutting by means of hf resectoscope implements of the state of the art in body cavities filled with an electrically conducting fluid is impossible, or only possible in an unsatisfactory manner.
The state of the art meets this problem by typically using electrically poorly conducting fluids when rinsing. It must be considered, however, that blood vessels are opened during resection and that part of the fluid inevitably enters the blood circulation of the patient. As a result, the patient may experience a complex of symptoms, also known as the TUR [transurethral resection] syndrome, such as vomiting, heart arrhythmia, kidney failure, shock. Therefore, using electrically poorly conducting fluids as rinses appears inappropriate, especially when it is realized that the above-noted reactions arise less intensely, sometimes not at all, when the isotonic fluids are used.
Therefore, an objective of the present invention is to create an hf resectoscope implement that overcomes the above difficulties and is optimized for the resection of body tissue in a body cavity filled with an electrically well-conducting fluid.
The effectiveness and, hence, an advantage of the present invention is an insulator structure, hereafter xe2x80x9cinsulatorxe2x80x9d, between the cutting electrode and the neutral one, that hampers the straight current between the two electrodes. Hence, the present invention reduces current flow directly between the electrodes, so that a larger portion of the supplied hf power is fed from the cutting electrode into the body tissue and there into cutting work. Vice-versa, less power is required by the implement of the invention relative to those of the state of the art to attain the cutting.
The basic idea of mounting an insulator between the active and the neutral electrode is known from the extra-species patent document WO 97/24993 which, in its FIG. 9, shows an implement comprising a rolling, spherical electrode of vaporization mounted in rotatable manner on a support. The ball""s axis of rotation is perpendicular to the support""s longitudinal axis. A hemispheric insulator, which also rests on the support, is mounted a slight distance above the ball. The neutral electrode is mounted on the insulator side, which is away from the vaporization electrode. In this manner a lesser straight current is attained between the active electrode and the neutral one. However, this design masks much of the field of view otherwise available to the surgeon. This drawback is inherent when using a spherical electrode.
The neutral electrode of the bipolar hf implement may, in principle, be mounted anywhere on the loop support. In further accordance with the present invention, however, the neutral electrode is configured distally at the loop support. This feature offers the advantage that when the implement is inserted into the stem tube of the resectoscope it need not move past the observation or illumination optics mounted in the stem tube. Instead, if the implement is properly dimensioned, the implement will be distally in front of the optics when it is inserted. In order to prevent arcing, care must be taken that the neutral electrode does not touch the optics. It is understood that the insulator must also be mounted distally at the loop support so that it can shield the electrodes from each other.
The cutting electrode, the insulator and the neutral electrode all are mounted on the loop support and held in place by the loop support. In the most general design, the three elements may be mounted in a mutually independent manner on the loop support, for instance by means of arms spreading from the loop support. Such a feature, however, is both uneconomical as regards manufacture and of low mechanical strength. Therefore, in accordance with another feature of the present invention, the neutral electrode is mounted directly on the insulator side away from the cutting electrode. Accordingly, the insulator supports the neutral electrode and imparts mechanical strength to the neutral electrode while improving the shielding geometry.
The geometry of the neutral electrode is widely arbitrary. However, in accordance with another feature of the invention, the-neutral electrode is mounted face-to-face or surface-on-surface to the insulator to be better held in place. Moreover, the topological design of the neutral electrode offers the advantage that current from the cutting electrode into the tissue and from there back to the neutral electrode is spread out over a large area and, hence, can enter the neutral electrode at low current density. This feature also means that, in the event of accidental contact of the topological neutral electrode with the body tissue, the consequence shall be only slight on this tissue. Additionally, the shielding geometry is improved.
The mechanical strength of the neutral electrode affixation and the shielding geometry may be improved further in that, according to another aspect of the invention, the neutral electrode is, to some extent, embedded in the insulator. This feature, furthermore, assures that the neutral electrode cannot make contact with the stem or the optics during retraction into the resectoscope.
However, a problem arises if the neutral electrode is fully inserted into the insulator. Namely, when the active electrode reaches the resectoscope""s cutting edge, the neutral electrode, on one hand, is masked by the insulator and, on the other hand, is masked by the distal end zone of the resectoscope stem, which usually is insulating. Consequently, the current is interrupted and, with it, the cutting action before the cutoff strip of tissue has been separated at the cutting edge.
In further accordance with the present invention, this difficulty is averted in a simple and advantageous manner by the neutral electrode comprising a distal zone which is not masked by the insulator. This zone is left uncovered also by the cutting electrode in the inserted state (i.e., when reaching the cutting edge of the resectoscope) and, hence, it is freely accessible to the return current. Thus, the current is uninterrupted, and the strip of body tissue can be separated at the cutting edge.
The insulator may be a flat plate. However, according to another feature of the invention, the insulator has a curvature that is advantageously inverted relative to that of the cutting electrode. This curvature improves the surgeon""s view through the insulator and the cutting electrode. Also, the inserted electrode is more easily guided over the resectoscope optics, especially when the optics is configured eccentrically above the resectoscope center axis.
The loop support holding the cutting electrode may be a single arm. In this case the electrodes are termed single bar electrodes. Typically, however, the loop support at the distal end is bifurcated to form two parallel bars. The cutting electrode, also referred to as the cutting loop, is substantially semi-circular and held in place between the two bars at a slant to the loop support""s longitudinal axis. As a rule, the plane of the loop is approximately perpendicular to the loop support""s longitudinal axis. However, the invention is not restricted to such a constraint and also includes slant angles other than 90xc2x0.
As regards the bifurcated loop supports, the present invention advantageously proposes distally adjoining the insulator to both bars. In this manner the insulator assures good mechanical strength of the distal zones of the hf resectoscope implement. Preferably, the insulator curvature is inverted relative to that of the cutting electrode resting on the bars of bifurcated loop supports. In this manner a free central zone remains between the cutting electrode and the insulator to allow unhampered viewing by the surgeon of the field of surgery.
In accordance with further features of the present invention, the axial projection of the cutting electrode together with that of the curved insulator bearing the neutral electrode essentially subtend or define a circle. It is understood that the circle diameter must be slightly less than the inside diameter of the resectoscope""s stem tube. Again, it is understood that in resectoscopes in which the stem tube exhibits an oval cross-section, the above axial projection will also be oval. These advantages are those already cited in the preceding paragraph, in particular as regards the surgery field of view.
In further accordance with the present invention, the insulator is integral and consists of a segment, a curvature of which is inverted relative to that of the cutting electrode, and a segment, which is shaped like the cutting electrode and mounted distally from it. Therefore, the insulator, per se, already substantially subtends a ring or circle. This feature, in conjunction with affixing the cutting electrode to the insulator segment and closely adjoining the insulator segment, contributes to high mechanical strength. The service life of the electrodes of the invention is very long because the cutting loop zone, which is especially stressed when the hf implement is working, is mechanically reinforced by the lower insulator segment. Additional advantages relate to implement installation and advantageous shielding by the insulator of the cutting loop.
In further accordance with the present invention, the cutting electrode at its lower zone assumes the shape of a wire flattened into a lamella. The lamella is mounted on the outside of the insulator segment which closely adjoins the cutting electrode. This mechanically-strong configuration allows coagulating by means of the lower side of the lamellar strip while the top side is shielded by the insulator. Accordingly, the insulator of the invention shields those parts of the cutting electrode which are not, nor should be, in contact with the tissue and, furthermore, reduces substantially further the current straight between the cutting and neutral electrodes.